Al2O3-Y-TZP/Al2O3 functionally graded composites of tubular shape from nano-sols using double-step electrophoretic deposition

Al2O3-Y-TZP/Al2O3 functionally graded composites of tubular shape incorporating a very tough central layer with graded composition (Al2O3-Y-TZP) and a hard outer surface layer of pure alumina were produced from nano-size sols using electrophoretic deposition (EPD) in an attempt to generate a continuously inhomogeneous property variation across the final component and to control the microstructure at a nanometer scale. It is shown that hardness, fracture toughness and alumina grain size within the graded layer are controlled by the volume fraction of TZP grains and the highest volume fraction (71%) of TZP phase provides a fracture toughness value of 7.1 MPa m(1/2) and Vicker's hardness of 10.4 GPa whilst the lowest volume fraction (13%) results in obtaining a fracture toughness value of 3.8 Wa m(1/2) and hardness value of 15.7 GPa. The pure alumina surface layer (100 pm in thickness) with a high hardness value of 19.4 GPa is considered to be beneficial for tribological applications where high wear resistance is required. (C) 2003 Elsevier Science Ltd. All rights reserved.